Hieroglyph 3 is an open source rendering framework written in C++, which uses Direct3D 11 to perform a variety of complex rendering operations. The library was written primarily by Jason Zink, with contributions also provided by Matt Pettineo and Jack Hoxley. The primary goals of the framework are to provide an easy to use, modular API that can efficiently utilize the advanced feature set of Direct3D 11.
A wide variety of rendering algorithms have already been implemented using the framework, which can be seen on the samples page. In contrast to many other frameworks, Hieroglyph 3 allows you to implement your own rendering systems with a minimal amount of work. This makes it a good candidate for prototyping new algorithms, or experimenting with existing ones.
The library is actively maintained, and the latest development snapshot can be downloaded from the Hieroglyph 3 codeplex page. The issue tracker and discussions areas of the codeplex page are best places to get help if you have questions about the engine. I am also active on the GameDev.net forums, so that is another possible avenue to ask some questions.